Cymothoa exigua is a parasitic crustacean that attaches itself to the tongue of the spotted rose snapper and feeds on its blood. Eventually, the organ atrophies, and then something remarkable happens: C. exigua replaces the fish’s tongue with its own body by attaching to the muscles of the tongue stub. The fish is able to use the parasite just like a normal tongue, apparently without any further damage. Are there any other cases of a parasite functionally replacing a host organ? Discuss
Source: The Free Dictionary